WEP encryption was introduced in 1999 for both data privacy and authentication. WEP open system authentication is based on request and grant. It is essentially no authentication.
WEP shared key authentication is based on request, challenge, challenge response, grant/deny. Before long WEP shared key authentication was found to be flawed and worse than open system authentication because it exposed the WEP key used for both initial authentication and ongoing data privacy.
The fix was to simply not use WEP shared key authentication - ever again. After the 802.11i amendment in 2004 the standard includes an optional second stage of authentication.